TOPOPLAN Report Summary

The controlled synthesis of nanoparticles in the form of spheres, rods and wires has led to a variety of applications. Much wider use e.g. in integrated devices requires a precise placement and alignment relative to neighboring particles or other functional structures on the substrate. A potential solution to this challenge is to use top-down methods to guide placement and orientation. Ideally, this is achieved for a wide range of particle shapes, a so far unresolved challenge. In this project we established a new tool, called the nanofluidic confinement apparatus, for the control, manipulation and immobilization of nanoscale particles in a nanofluidic environment. The tool allows us to generate a tunable energy landscape for nanoparticles between two confining surfaces in liquid. The shape of the energy landscape is determined by the local three-dimensional topography of the confining surfaces. We demonstrated that trapping potentials can be shaped to fit to a wide range of particle shapes, such as gold spheres or rods, 5 μm long and 30 nm wide nanowires and even protein membranes. The trapping energies were measured to exceed the thermal energies governing Brownian motion and trap and orient particles reliably. After trapping, the particles were transferred in a subsequent step onto the substrate by approaching the two surfaces. At sufficiently small gap distances the particles are transferred and immobilized on the receiving substrate. Particle placement accuracies of less than 10 nm were achieved.Furthermore, the tunable energy landscape was found to have another highly interesting application potential for the directed transport and sorting of nanoparticles. It allowed us to establish so called rocked Brownian Motors for nanoparticles, theoretically proposed by Magnasco in the 90s. We could verify the working principle experimentally and observed transport speeds of up to 50 μm per second without a net flow of the fluid. Moreover, as theoretically proposed, we could exploit the highly non-linear transport scheme of the motors for an efficient separation of 60 and 100 nm particles within seconds. Accordingly, highly selective transport for nanoparticles without fluid flow became possible with a range of potential lab on chip applications ranging from highly selective particle separation to accumulation and detection of ultra-small particle concentrations.For the particle placement goal of this project, this efficient transport mechanism provides an elegant means for the targeted transport of the nanoparticles to their deposition sites. In a wider context, we have established two novel methods for the nanofluidic transport and separation as well as for the placement of nanoparticles on surfaces. Combining the in-situ sorting potential of the particles using the Brownian motor schemes and the tens of nanometer precise placement will enable researchers to fabricate complex devices without breaking the fluidic environment. The newly developed methods open up exciting possibilities, in particular for the assembly of bio-inspired functional devices involving tailored protein membranes.